Human serum albumin ("HSA") is the major protein component of plasma and consists of a single polypeptide chain of 585 amino acids, having a molecular weight of about 66,000 daltons. Its 17 intramolecular disulfide bridges contribute to the high stability of the albumin molecule.
The primary function of albumin in plasma is maintenance of the colloid osmotic pressure within the blood vessel. Furthermore, the protein acts as a carrier of several ligands, for instance bilirubin and fatty acids. (See reviews by F. Rothstein, V. M. Rosenoer and W. L. Hughes, in Albumin Struct. Funct. Uses (1977) 7-25; U. Kragh-Hansen, Pharmacol. Rev. (1981) 33:17-53; T. Peters Jr., in Adv. Prot. Chem. (1985) 37:161-245.)
Purified serum albumin is indicated for the prevention and treatment of hypovolemic shock, in conditions where there is severe hypoalbuminemia, as an adjunct in hemodialysis and in cardiopulmonary bypass procedures and in conjunction with exchange transfusion in the treatment of neonatal hyperbilirubinemia.
For the large scale purification of HSA from plasma or placenta, precipitation methods using ethanol, polyethyleneglycol, trichloroacetic acid or ammonium sulphate together with Rivanol.RTM. and/or liquid chromatography methods are frequently applied. (See for the latter, J. Saint-Blancard, J. M. Kirzin, P. Riberon, F. Petit, J. Fourcart, P. Girot and E. Boschetti, Anal. Chem. Symp. Ser. (1982) 9:305-312; J. M. Curling, in Methods of Plasma Protein Fractionation (1980) 77-91; M. J. Harvey, in Methods of Plasma Protein Fractionation (1980) 189-200; N. E. Schultze and J. F. Heremans, Mol. Biol. Hum. Prot. (1966) 1:261-270; J. Liautau, J. Pla, A. Debrus, P. Gattel, R. Plan and L. Peyron, 13 th Int. Congr. IABS (1973) 27:107-114; Hao, Y-L, Vox Sang (1985) 49:1-8; and U.S. Pat. No. 4,228,154.)
On a laboratory scale the application of affinity chromatography for the purification of serum albumin has been described by T. Peters Jr., H. Taniuchi and C.B. Anfinsen Jr., in J. Biol. Chem. (1973) 248(7):2447-2451; A. Wichman and L-O. Andersson, Biochim. Biophys. Acta (1974) 372:218-224; and A. Aslam, D.J. Jones and T.R. Brown, Anal. Biochem. (1976) 75:329-335.
Since large amounts of serum albumin are necessary for therapy and the source of serum albumin (plasma) is limited, other techniques have been sought to produce HSA in large quantities. Successes have been reported in the production of HSA by fermentation using transformed microorganisms or cell lines made by recombinant DNA techniques. See, for example, EP-A-0073646.
However, one of the major problems in the purification of serum albumin produced by fermentation using transformed cells is the presence of contaminating components from the growth medium (fermentation broth) or cell lysate, which have to be removed in order to obtain purified, homogeneous serum albumin.
These contaminants are for example foreign proteins which would be expected to produce an immunological response. Administration of contaminated HSA could lead to shock. These contaminants are totally different from those which occur during fractionation of the serum albumin from plasma or placenta. This means that the purification methods developed for HSA from natural sources cannot be extrapolated to the purification of recombinant serum albumin. Practical processes for large scale purification of human serum albumin produced by transformed microorganisms or cell lines have not been published so far and are not yet available.